Electrode sheet drying apparatus

ABSTRACT

An electrode sheet drying apparatus includes a plurality of hot air blowers each having a nozzle. The nozzle has a first hot air guide having a first guide surface, a second hot air guide having a second guide surface. The nozzle is configured to blow band hot air toward an obliquely upstream side. An angle formed between the first guide surface and an undried active material layer is set to an angle at which the band hot air travels toward an upstream side along the undried active material layer over a distance longer than or equal to 15 times as large as a gap from a first upstream-side edge to the undried active material layer even without a spread prevention part.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2020-096701 filed on Jun. 3, 2020, incorporated herein by reference inits entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to an electrode sheet drying apparatusthat heats and dries an undried active material layer provided on a bandcurrent collector foil in an undried electrode sheet with hot air whileconveying the undried electrode sheet in a longitudinal direction of theundried electrode sheet.

2. Description of Related Art

A band electrode sheet in which a band active material layer provided ona band current collector foil extends in the longitudinal direction ofthe current collector foil is known as an electrode sheet used as apositive electrode sheet or negative electrode sheet of a battery orcapacitor. Such a band electrode sheet is manufactured by, for example,the following technique. An active material paste containing activematerial particles and the like dispersed in a dispersion medium isprepared, and then the active material paste is applied onto a currentcollector foil to form a band undried electrode sheet in which a bandundried active material layer is provided on the current collector foil.After that, the undried electrode sheet is conveyed into an electrodesheet drying apparatus, and hot air is blown onto the undried activematerial layer while the undried electrode sheet is being conveyed inthe longitudinal direction inside the electrode sheet drying apparatus.Thus, the undried active material layer is heated and dried, and anactive material layer is formed. For example, Japanese Unexamined PatentApplication Publication No. 2013-068394 (JP 2013-068394 A) is anexisting technique related to such an electrode sheet drying apparatus.

An electrode sheet drying apparatus 900 described in JP 2013-068394 Aincludes a plurality of hot air blowers 930 inside (see FIG. 9). The hotair blowers 930 each are located in a first thickness direction GH1(upward in FIG. 9) with respect to an undried electrode sheet 1A. Thefirst thickness direction GH1 is directed from a current collector foil3 toward an undried active material layer 5 x in a thickness directionGH of the undried electrode sheet 1A. The hot air blowers 930 arearranged in a conveying direction CH (longitudinal direction EH) at apredetermined pitch. Each of the hot air blowers 930 includes areservoir main body 931, and a nozzle 933. The reservoir main body 931defines a reservoir space for temporarily holding hot air HAb. Thenozzle 933 blows the hot air HAb in the reservoir main body 931 towardan obliquely upstream side IH (a second thickness direction GH2 oppositefrom the first thickness direction GH1 in the thickness direction GH andan upstream side CH1 in the conveying direction CH, and, in FIG. 9, alower left direction) as band hot air HA.

The reservoir main body 931 has a rectangular parallelepiped box shape.The reservoir main body 931 has a first wall 931 a located in the firstthickness direction GH1, a second wall 931 b located in the secondthickness direction GH2, an upstream-side wall 931 c located on theupstream side CH1 in the conveying direction CH, a downstream-side wall931 d located on a downstream side CH2 in the conveying direction CH, awidth-side wall (not shown) located on the near side of the drawingsheet in FIG. 9, and a width-side wall 931 f located on the far side ofthe drawing sheet in FIG. 9. On the other hand, the nozzle 933 isprovided on the downstream side CH2 of the second wall 931 b and in thesecond thickness direction GH2 with respect to the downstream-side wall931 d. The nozzle 933 extends in a width direction FH (in FIG. 9, thedirection perpendicular to the drawing sheet) of the undried electrodesheet 1A. The nozzle 933 blows band hot air HA wide in the widthdirection FH toward the obliquely upstream side IH.

In each of the thus configured hot air blowers 930, the second wall 931b of the reservoir main body 931 is present on the upstream side CH1 ofthe nozzle 933, so the band hot air HA blown out from the nozzle 933 isprevented by the second wall 931 b from spreading in the first thicknessdirection GH1. In other words, the second wall 931 b of the reservoirmain body 931 serves as a spread prevention part that prevents thespread of blown band hot air HA in the first thickness direction GH1.Then, the band hot air HA passing through the clearance between thesecond wall (spread prevention part) 931 b and the undried activematerial layer 5 x of the undried electrode sheet 1A further travelsalong the undried active material layer 5 x toward the upstream sideCH1. In this way, by allowing the band hot air HA to flow along theundried active material layer 5 x toward the upstream side CH1, it ispossible to efficiently dry the undried active material layer 5 x.

SUMMARY

However, the hot air blower 930 has the second wall (spread preventionpart) 931 b on the upstream side CH1 of the nozzle 933, so the overallsize Lb of the hot air blower 930 in the conveying direction CH islarge. For this reason, in arranging the hot air blowers 930 in theconveying direction CH, the flexibility of arrangement of the hot airblowers 930 is low. In other words, when the hot air blowers 930 arearranged in the conveying direction CH to successively blow the band hotair HA onto the undried active material layer 5 x to quickly dry theundried active material layer 5 x, the gap between any adjacent hot airblowers 930 needs to be widened; however, this leads to an increase inthe size of the electrode sheet drying apparatus 900 in the conveyingdirection.

The disclosure provides an electrode sheet drying apparatus with a highflexibility of arrangement of hot air blowers, for example, with areduced size in a conveying direction while a plurality of hot airblowers is arranged in the conveying direction.

An aspect of the disclosure provides an electrode sheet drying apparatusthat heats and dries an undried active material layer provided on a bandcurrent collector foil in an undried electrode sheet while conveying theundried electrode sheet in a longitudinal direction of the undriedelectrode sheet. The electrode sheet drying apparatus includes aplurality of hot air blowers each located in a first thickness directionwith respect to the undried electrode sheet. The first thicknessdirection is directed from the current collector foil toward the undriedactive material layer in a thickness direction of the undried electrodesheet. The plurality of hot air blowers is arranged in a conveyingdirection of the undried electrode sheet at a predetermined pitch. Eachof the hot air blowers includes a nozzle configured to blow band hot airin a second thickness direction opposite from the first thicknessdirection in the thickness direction and toward an obliquely upstreamside that is an upstream side in the conveying direction. The band hotair spreads in a width direction of the undried electrode sheet. Thenozzle includes a first hot air guide having a first guide surface thatadvances in the first thickness direction toward a downstream side inthe conveying direction, and a second hot air guide located in thesecond thickness direction with respect to the first guide surface andhaving a second guide surface facing and parallel to the first guidesurface. The nozzle is configured to blow the band hot air toward theobliquely upstream side from between a first upstream-side edge that isan edge at the upstream side of the first guide surface and a secondupstream-side edge that is an edge at the upstream side of the secondguide surface through between the first guide surface and the secondguide surface. An angle formed between the first guide surface or thesecond guide surface and the undried active material layer is set to anangle at which the blown band hot air travels toward the upstream sidealong the undried active material layer over a distance longer than orequal to 15 times as large as a gap from the first upstream-side edge tothe undried active material layer even without a spread prevention partthat prevents spread of the band hot air in the first thicknessdirection being provided at the upstream side of the nozzle.

In the above-described electrode sheet drying apparatus, band hot airblown from the nozzle of each hot air blower toward the obliquelyupstream side travels toward the upstream side in the conveyingdirection along the undried active material layer over a long distance,specifically, a distance longer than or equal to 15 times as large asthe above-described gap. Therefore, it is possible to efficiently drythe undried active material layer. Moreover, each hot air blower doesnot need a spread prevention part that prevents spread of band hot airin the first thickness direction (direction away from the undried activematerial layer) on the upstream side of the nozzle. Therefore, incomparison with a hot air blower having a spread prevention part, theoverall size of the hot air blower in the conveying direction isreduced. For this reason, the flexibility of arrangement of hot airblowers is increased, for example, the size of the electrode sheetdrying apparatus in the conveying direction is reduced by arranging theplurality of hot air blowers at a narrow pitch.

Examples of a band electrode sheet formed by drying the undriedelectrode sheet include an electrode sheet used for batteries, such aslithium ion secondary batteries, and an electrode sheet used forcapacitors, such as lithium ion capacitors. The electrode sheet may be apositive electrode sheet that makes up a positive electrode or anegative electrode sheet that makes up a negative electrode.

Examples of the undried active material layer include a band undriedactive material layer provided on a band current collector foil andextending in a longitudinal direction of the current collector foil, andan undried active material layer in such a form that a plurality ofundried active material layers is arranged in the longitudinal directionat a predetermined pitch. The undried active material layer may also bean undried active material layer formed by applying an active materialpaste containing active material particles and the like dispersed in adispersion medium onto a current collector foil, or an undried activematerial layer formed in such a manner that an aggregate of wettingparticles obtained by mixing active material particles and the like witha dispersion medium and granulating the mixture is prepared and then theparticle aggregate is rolled and transferred onto a current collectorfoil.

The phrase “band hot air travels toward the upstream side along theundried active material layer over a distance” means the following. Whenthe flow velocity distribution of band hot air in the thicknessdirection on the upstream side of the first upstream-side edge of thenozzle in the conveying direction is obtained, band hot air travelstoward the upstream side over the distance while maintaining the flowvelocity distribution in which the flow velocity of band hot airdecreases as a point advances in the first thickness direction (as apoint shifts away from the undried active material layer); conversely,the flow velocity distribution in which the flow velocity of band hotair increases as a point advances in the second thickness direction (asa point approaches the undried active material layer), except for anear-surface region within 1 mm from the surface of the undried activematerial layer in the first thickness direction.

In the electrode sheet drying apparatus, the angle may fall within arange from 5° to 45°, the gap may fall within a range from 3 mm to 10mm, and an initial flow velocity of the band hot air blown from thenozzle may fall within a range from 40 m/s to 80 m/s.

In the electrode sheet drying apparatus, the angle formed between theundried active material layer and each of the first guide surface andsecond guide surface of the nozzle falls within a range from 5° to 45°,the gap from the first upstream-side edge of the nozzle to the undriedactive material layer falls within a range from 3 mm to 10 mm, and theinitial flow velocity of the band hot air falls within a range from 40m/s to 80 m/s. With this configuration, band hot air blown from thenozzle tends to flow toward the upstream side along the undried activematerial layer over a long distance.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like signs denote likeelements, and wherein:

FIG. 1 is a perspective view of a band electrode sheet according to anembodiment;

FIG. 2 is a flowchart of a manufacturing method for the band electrodesheet according to the embodiment;

FIG. 3 is a diagram showing the whole of an electrode sheet dryingapparatus according to the embodiment;

FIG. 4 is a plan view of a hot air blower and an undried one-sideelectrode sheet according to the embodiment when viewed from a side in afirst thickness direction;

FIG. 5 is a cross-sectional view of the hot air blower and the undriedone-side electrode sheet according to the embodiment when viewed in awidth direction;

FIG. 6 is a diagram illustrating the flow velocity distribution of bandhot air in a thickness direction according to the embodiment;

FIG. 7 is a graph showing the amount of residual dispersion mediumremaining in an active material layer of each of one-side electrodesheets according to Examples 1 to 3 and Comparative Examples 1 and 2;

FIG. 8 is a diagram illustrating the flow velocity distribution of bandhot air in the thickness direction according to the comparativeexamples; and

FIG. 9 is a cross-sectional view of a hot air blower and an undriedelectrode sheet according to an existing art when viewed in a widthdirection.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the disclosure will be described withreference to the accompanying drawings. FIG. 1 is a perspective view ofa band electrode sheet 1 according to the present embodiment. The bandelectrode sheet 1 is used to manufacture square sealed lithium ionsecondary batteries that are mounted on vehicles, such as hybridvehicles, plug-in hybrid vehicles, and electric vehicles, and otherdevices. Specifically, the band electrode sheet 1 is a band positiveelectrode sheet used to manufacture a flat wound or stacked electrodeassembly that is a component of a battery. Hereinafter, description willbe made on the assumption that the longitudinal direction EH, widthdirection FH, and thickness direction GH of the band electrode sheet 1are defined as the directions shown in FIG. 1.

The band electrode sheet 1 includes a current collector foil 3 made froma band aluminum foil extending in the longitudinal direction EH. On afirst main surface 3 a of the current collector foil 3, an activematerial layer 5 is provided in a band shape in the longitudinaldirection EH in an area extending in the longitudinal direction EH inthe middle in the width direction FH. On an opposite-side second mainsurface 3 b of the current collector foil 3, an active material layer 15is provided in a band shape in the longitudinal direction EH also in anarea extending in the longitudinal direction EH in the middle in thewidth direction FH. The active material layers 5, 15 each are notprovided on portions extending in the longitudinal direction EH at bothends in the width direction FH on the current collector foil 3. Theportions extending in the longitudinal direction EH at both ends in thewidth direction FH are exposed portions 3 r from which the currentcollector foil 3 is exposed in the thickness direction GH. The activematerial layers 5, 15 are made up of active material particles,electrically conductive particles, and a binder. In the presentembodiment, lithium transition metal composite oxide particles,specifically, lithium nickel cobalt manganese oxide particles, are usedas active material particles. Acetylene black (AB) particles are used aselectrically conductive particles. Polyvinylidene difluoride (PVDF) isused as a binder.

Next, a manufacturing method for the band electrode sheet 1 will bedescribed (see FIG. 2 to FIG. 6). Initially, in first electrode formingstep S1 (see FIG. 2), an undried one-side electrode sheet (undriedelectrode sheet) 1A having a band undried active material layer 5 x thatwill be the active material layer 5 after being dried is formed on thefirst main surface 3 a of the current collector foil 3. Specifically, inadvance of performing the first electrode forming step S1, an electrodepaste PE is prepared in advance. The electrode paste PE is formed bymixing active material particles, electrically conductive particles, abinder, and a dispersion medium (in the present embodiment, N-methylpyrrolidone (NMP)) and dispersing the active material particles, theelectrically conductive particles, and the binder in the dispersionmedium. The electrode paste PE has a solid content concentration NV of62.5 wt % in the present embodiment.

In the first electrode forming step S1, the undried active materiallayer 5 x is formed by applying the electrode paste PE onto the firstmain surface 3 a of the current collector foil 3. Specifically, thecurrent collector foil 3 unwound from an unwind roll (not shown) isconveyed in the longitudinal direction EH by a plurality of conveyancerolls (not shown). Then, the undried active material layer 5 x iscontinuously formed in a band shape on the first main surface 3 a of thecurrent collector foil 3 by discharging the electrode paste PE in apredetermined amount from a coating die (not shown) to a middle part inthe width direction FH on the first main surface 3 a of the currentcollector foil 3. The undried active material layer 5 x has a thicknesst of 60 μm in the present embodiment.

Subsequently, in first drying step S2 (see FIG. 2), the undried activematerial layer 5 x is heated and dried with band hot air HA while theundried one-side electrode sheet 1A obtained in the first electrodeforming step S1 is being conveyed in the longitudinal direction EH.Thus, the active material layer 5 is formed. The first drying step S2 isperformed by using the electrode sheet drying apparatus 100 (see FIG. 3to FIG. 6). The electrode sheet drying apparatus 100 is made up of adrying chamber 110, a plurality of conveyance rolls 120 that convey theundried one-side electrode sheet 1A, a plurality of hot air blowers 130that blow band hot air HA toward the undried one-side electrode sheet1A, a duct 150 that guides hot air HAb to the hot air blowers 130, a hotair generating unit 160 that generates hot air HAb, and the like.

The drying chamber 110 (see FIG. 3) has a box shape isolated from theoutside by a wall 111. The drying chamber 110 has a carry-in port 111 iand a carry-out port 111 j. The carry-in port 111 i is used to conveythe undried one-side electrode sheet 1A from the outside into the dryingchamber 110. The carry-out port 111 j is used to carry out a driedone-side electrode sheet 1B from the drying chamber 110 to the outside.The conveyance rolls 120 (see FIG. 3) are disposed in the drying chamber110 and driven by a motor (not shown). The conveyance rolls 120 conveythe undried one-side electrode sheet 1A in the longitudinal direction EHwhile being in contact with the current collector foil 3 of the undriedone-side electrode sheet 1A. In each of FIG. 3 to FIG. 6, the right andleft direction is the conveying direction CH, the left side is theupstream side CH1 of the conveying direction CH, and the right side isthe downstream side CH2 of the conveying direction CH. In FIG. 3, FIG.5, and FIG. 6, the upward direction is the first thickness direction GH1from the current collector foil 3 toward the undried active materiallayer 5 x in the thickness direction GH of the undried one-sideelectrode sheet 1A, and the downward direction is the second thicknessdirection GH2 opposite from the first thickness direction GH1 in thethickness direction GH.

The hot air blowers 130 (see FIG. 3 to FIG. 6) each are located in thefirst thickness direction GH1 with respect to the undried one-sideelectrode sheet 1A to be conveyed by the conveyance rolls 120 in thedrying chamber 110 and are arranged in the conveying direction CH(longitudinal direction EH) at a predetermined pitch. Each of the hotair blowers 130 communicates with the duct 150 (described later) in thefirst thickness direction GH1 and connected to the hot air generatingunit 160 (described later) via the duct 150. With this configuration,hot air HAb generated by the hot air generating unit 160 is oncesupplied to the hot air blowers 130 through the duct 150 and then blownto the outside as band hot air HA.

Each hot air blower 130 includes a reservoir main body 131 and a nozzle133. The reservoir main body 131 defines a reservoir space fortemporarily holding hot air HAb. The nozzle 133 blows the held hot airHAb to the outside as band hot air HA in a band shape. The reservoirmain body 131 has a rectangular parallelepiped box shape and has a firstwall 131 a, an upstream-side wall 131 c, a downstream-side wall 131 d, awidth-side wall 131 e, and a width-side wall 131 f. The first wall 131 aof the reservoir main body 131 has a communication hole thatcommunicates with the duct 150 (described later), and the communicationhole is not shown in FIG. 4 to FIG. 6.

The first wall 131 a is located in the first thickness direction GH1 anddisposed parallel to the undried one-side electrode sheet 1A to beconveyed by the conveyance rolls 120 (disposed perpendicularly to thethickness direction GH). The upstream-side wall 131 c is located at theupstream side CH1 in the conveying direction CH and disposedperpendicularly to the conveying direction CH. The downstream-side wall131 d is located at the downstream side CH2 in the conveying directionCH and disposed perpendicularly to the conveying direction CH. Thewidth-side walls 131 e, 131 f are respectively located at both sides inthe width direction FH of the undried one-side electrode sheet 1A anddisposed perpendicularly to the width direction FH.

Each nozzle 133 is configured to blow band hot air HA spreading in thewidth direction FH of the undried one-side electrode sheet 1A toward anobliquely upstream side IH (in a lower left direction in FIG. 3, FIG. 5,and FIG. 6) that is the upstream side CH1 in the conveying direction CHand in the second thickness direction GH2. The nozzle 133 is provided onone side of the reservoir main body 131 in the second thicknessdirection GH2, and extends in the width direction FH. Specifically, thenozzle 133 is made up of a first hot air guide 134 and a second hot airguide 135 (see FIG. 5 and FIG. 6).

The first hot air guide 134 and the second hot air guide 135 each have arectangular plate shape extending in the width direction FH and aredisposed parallel to each other with a gap. The first hot air guide 134extends from an end 131 ct of the upstream-side wall 131 c in the secondthickness direction GH2 in a direction opposite from the obliquelyupstream side IH (that is, in a right upper direction in FIG. 5 and FIG.6) such that a point advances in the first thickness direction GH1toward the downstream side CH2. In the present embodiment, a mainsurface of the first hot air guide 134, facing in the second thicknessdirection GH2, is a first guide surface 134 n. In the first guidesurface 134 n, a point advances in the first thickness direction GH1toward the downstream side CH2.

On the other hand, the second hot air guide 135 extends from an end 131dt of the downstream-side wall 131 d in the second thickness directionGH2 toward the obliquely upstream side IH such that a point advances inthe second thickness direction GH2 toward the upstream side CH1. In thepresent embodiment, a main surface of the second hot air guide 135,facing in the first thickness direction GH1, is a second guide surface135 n. The second guide surface 135 n is located in the second thicknessdirection GH2 with respect to the first guide surface 134 n and facesparallel to the first guide surface 134 n.

An opening width M of the nozzle 133, perpendicular to the widthdirection FH and the direction directed toward the obliquely upstreamside IH, is 5 mm in the present embodiment. A gap G from a firstupstream-side edge 134 nt that is an edge of the first guide surface 134n at the upstream side CH1 to the undried active material layer 5 xfalls within a range from 3 mm to 10 mm (G=5 mm in the presentembodiment). A gap K from a second upstream-side edge 135 nt that is anedge of the second guide surface 135 n at the upstream side CH1 to theundried active material layer 5 x is also 5 mm in the presentembodiment.

An angle α formed between each of the first guide surface 134 n andsecond guide surface 135 n of the nozzle 133 and the undried activematerial layer 5 x (hereinafter, also simply referred to as the angle αof the nozzle 133) falls within a range from 5° to 45° (α=30° in thepresent embodiment). In the present embodiment, the angle α of thenozzle 133 is set to an angle at which, even when a spread preventionpart that prevents spread of band hot air HA in the first thicknessdirection GH1 is not provided on the upstream side CH1 of the nozzle133, blown band hot air HA travels toward the upstream side CH1 alongthe undried active material layer 5 x over the distance LS longer thanor equal to 15 times as large as the gap G (G=5 mm in the presentembodiment) (in the present embodiment, the distance LS is about 35times as large as the gap G: LS=about 175 mm).

With the thus configured hot air blower 130, hot air HAb supplied intothe reservoir main body 131 of the hot air blower 130 is blown as bandhot air HA from between the first upstream-side edge 134 nt of the firstguide surface 134 n and the second upstream-side edge 135 nt of thesecond guide surface 135 n toward the obliquely upstream side IH throughbetween the first guide surface 134 n and second guide surface 135 n ofthe nozzle 133. An initial flow velocity Vs of the band hot air HA fallswithin a range from 40 m/s to 80 m/s (Vs=60 m/s in the presentembodiment). The blown band hot air HA travels toward the upstream sideCH1 along the undried active material layer 5 x over a long distance L,that is, the distance LS of about 35 times as large as the gap G in thepresent embodiment.

FIG. 6 schematically shows the obtained results of the flow velocitydistribution of the band hot air HA in the thickness direction GH. InFIG. 6, the flow velocity V of band hot air HA within a near-surfaceregion SR 1 mm or less in the first thickness direction GH1 from asurface 5 xn of the undried active material layer 5 x is not shown. Bandhot air HA blown from the nozzle 133 at an initial flow velocity Vs of60 m/s gradually decreases its flow velocity V as the band hot air HAtravels toward the upstream side CH1 in the conveying direction CH. Theband hot air HA travels toward the upstream side CH1 over a distance LSof about 35 times as large as the gap G from the first upstream-sideedge 134 nt of the nozzle 133 to the undried active material layer 5 x(LS=G×35) while maintaining such a flow velocity distribution that theflow velocity V decreases as a point advances in the first thicknessdirection GH1 (as a point shifts away from the undried active materiallayer 5 x). In this way, in the electrode sheet drying apparatus 100 ofthe present embodiment, although no spread prevention part that preventsspread of band hot air HA in the first thickness direction GH1 isprovided on the upstream side CH1 of the nozzle 133, the band hot air HAtravels toward the upstream side CH1 along the undried active materiallayer 5 x over a long distance L, that is, a distance LS of about 35times as large as the gap G in the present embodiment.

The duct 150 is a flow passage of hot air HAb, connecting the hot airblowers 130 and the hot air generating unit 160 (described later). Theduct 150 is connected to each hot air blower 130 at the side of the hotair blower 130 in the first thickness direction GH1 in the dryingchamber 110 and connected to the hot air generating unit 160 outside thedrying chamber 110. Through the duct 150, hot air HAb generated by thehot air generating unit 160 is supplied to the hot air blowers 130. Thehot air generating unit 160 is disposed outside the drying chamber 110and communicates with the duct 150. The hot air generating unit 160includes an air blower fan (not shown) and a heater (not shown). The hotair generating unit 160 is configured to generate hot air HAb byincreasing the temperature of air flow generated by the air blower fanwith the heater. In the present embodiment, it is assumed that thetemperature of the hot air HAb is 180° C.

Next, the first drying step S2 using the electrode sheet dryingapparatus 100 will be described. The undried one-side electrode sheet 1Ais carried into the drying chamber 110 through the carry-in port 111 iin a state where the undried active material layer 5 x faces in thefirst thickness direction GH1 and the current collector foil 3 faces inthe second thickness direction GH2 and is conveyed in the longitudinaldirection EH by the conveyance rolls 120 in the drying chamber 110. Onthe other hand, band hot air HA spreading in the width direction FH isblown toward the obliquely upstream side IH from the nozzles 133 of thehot air blowers 130 provided in the first thickness direction GH1 withrespect to the undried one-side electrode sheet 1A.

The band hot air HA travels toward the upstream side CH1 along theundried active material layer 5 x over the distance LS longer than orequal to 15 times as large as the gap G (G=5 mm in the presentembodiment) from the first upstream-side edge 134nt of the nozzle 133 tothe undried active material layer 5 x (in the present embodiment, thedistance LS is about 35 times as large as the gap G: LS=about 175 mm).When such band hot air HA is blown from the nozzles 133 of the hot airblowers 130, the dispersion medium contained in the undried activematerial layer 5 x vaporizes, and the dried active material layer 5 iscontinuously formed. A band electrode sheet in which the active materiallayer 5 is formed on the first main surface 3 a of the current collectorfoil 3 is also referred to as one-side electrode sheet 1B. The one-sideelectrode sheet 1B is carried out to the outside of the drying chamber110 through the carry-out port 111 j of the drying chamber 110.

Subsequently, in second electrode forming step S3 (see FIG. 2), theone-side electrode sheet 1B is used, and an undried both-side electrodesheet (undried electrode sheet) 1C having a band undried active materiallayer 15 x that will be the active material layer 15 after being driedis formed on the second main surface 3 b of the current collector foil3. Specifically, as in the case of the first electrode forming step S1,the undried active material layer 15 x having a thickness t of 60 μm iscontinuously formed by applying an electrode paste PE onto the secondmain surface 3 b of the current collector foil 3.

Subsequently, in second drying step S4 (see FIG. 2), as in the case ofthe first drying step S2, by using the electrode sheet drying apparatus100 (see FIG. 3 to FIG. 6), the undried active material layer 15 x isheated and dried with band hot air HA while the undried both-sideelectrode sheet 1C is being conveyed in the longitudinal direction EH.Thus, the active material layer 15 is formed. In the second drying stepS4 as well, band hot air HA is blown toward the obliquely upstream sideIH from the nozzles 133 of the hot air blowers 130. The band hot air HAalso travels toward the upstream side CH1 along the undried activematerial layer 15 x over the distance LS longer than or equal to 15times as larger as the gap G (G=5 mm in the present embodiment) from thefirst upstream-side edge 134 nt of the nozzle 133 to the undried activematerial layer 15 x (in the present embodiment, the distance LS is about35 times as large as the gap G: LS=about 175 mm). A band electrode sheetin which the active material layer 5 is formed on the first main surface3 a of the current collector foil 3 and the active material layer 15 isformed on the second main surface 3 b is also referred to as both-sideelectrode sheet 1D.

Subsequently, in press step S5 (see FIG. 2), by using a roll pressmachine (not shown), roll press is applied to the both-side electrodesheet 1D in the thickness direction GH while the both-side electrodesheet 1D is being conveyed in the longitudinal direction EH. Thus, thedensities of the active material layers 5, 15 are increased. In thisway, the band electrode sheet 1 (see FIG. 1) is provided.

EXAMPLES 1 TO 3 AND COMPARATIVE EXAMPLES 1 AND 2

Next, the results of the tests carried out to examine the advantageouseffects of the disclosure will be described. In the tests, the dry stateof the active material layer 5 was obtained in the case where the angleα of the nozzle 133 of each hot air blower 130 (the angle α formedbetween each of the first guide surface 134 n and the second guidesurface 135 n and the undried active material layer 5 x) was set to adifferent angle in the electrode sheet drying apparatus 100 and theundried active material layer 5 x was dried with hot air.

Specifically, as in the case of the above-described embodiment, theundried one-side electrode sheet 1A in which the undried active materiallayer 5 x was provided on the current collector foil 3 was formed in thefirst electrode forming step S1, and then the active material layer 5was formed by heating and drying the undried active material layer 5 xwith band hot air HA in the first drying step S2. At this time, theangle α of each nozzle 133 was set to 5° in Example 1, 30° in Example 2as in the case of the embodiment, 45° in Example 3, 55° in ComparativeExample 1, and 65° in Comparative Example 2 (see FIG. 7).

For each of Examples 1 to 3 and Comparative Examples 1 and 2, the flowvelocity distribution of band hot air HA in the thickness direction GHwas obtained. As a result, in Examples 1 to 3, substantially the flowvelocity distribution shown in FIG. 6 was obtained. In each of Examples1 to 3, band hot air HA traveled toward the upstream side CH1 over thedistance LS longer than or equal to 15 times as large as the gap G fromthe first upstream-side edge 134 nt of each nozzle 133 to the undriedactive material layer 5 x while maintaining such a flow velocitydistribution that the flow velocity V of band hot air HA decreases as apoint advances in the first thickness direction GH1 except for thenear-surface region SR within 1 mm in the first thickness direction GH1from the surface 5 xn of the undried active material layer 5 x. In otherwords, in Examples 1 to 3, band hot air HA traveled toward the upstreamside CH1 along the undried active material layer 5 x over the longdistance LS longer than or equal to 15 times as large as the gap G.

On the other hand, in Comparative Examples 1 and 2, the flow velocitydistributions shown in FIG. 8 were obtained. In each of ComparativeExamples 1 and 2, part of band hot air HA, having the highest flowvelocity V, significantly separated in the first thickness direction GH1from the surface 5 xn of the undried active material layer 5 x beforereaching the distance LS longer than or equal to 15 times as large asthe gap G. Specifically, at, for example, an area of the distance L=G×10in FIG. 8, part of the band hot air HA, having the highest flow velocityV of 30 m/s to 40 m/s, is separated in the first thickness direction GH1from the undried active material layer 5 x, and part of the band hot airHA, having a flow velocity of 20 m/s to 30 m/s lower than the velocity Vof 30 m/s to 40 m/s, is present in the second thickness direction GH2with respect to the part having a flow velocity of 30 m/s to 40 m/s. Inthis way, in Comparative Examples 1 and 2, band hot air HA did nottravel toward the upstream side CH1 along the undried active materiallayer 5 x over the long distance L.

Next, for each of the one-side electrode sheets 1B of Examples 1 to 3and Comparative Examples 1 and 2, obtained in the first drying step S2,the amount (ppm) of residual dispersion medium remaining in the activematerial layer 5 was measured with gas chromatography. The results areshown by the graph in FIG. 7. As is apparent from the graph of FIG. 7,the amount of residual dispersion medium was less in Examples 1 to 3than in Comparative Examples 1 and 2. The reason causing such results ispresumed as follows.

In Examples 1 to 3, the flow velocity distributions of band hot air HAin the thickness direction GH each are substantially the flow velocitydistribution shown in FIG. 6, and band hot air HA travels toward theupstream side CH1 along the undried active material layer 5 x over thelong distance LS longer than or equal to 15 times as large as the gap G.Therefore, it is possible to efficiently dry the undried active materiallayer 5 x, so the amount of residual dispersion medium remaining in theactive material layer 5 was small. In contrast, in Comparative Examples1 and 2, the flow velocity distributions of band hot air HA in thethickness direction GH are the flow velocity distributions shown in FIG.8, and band hot air HA cannot travel toward the upstream side CH1 alongthe undried active material layer 5 x over the long distance L.Therefore, it is not possible to efficiently dry the undried activematerial layer 5 x, so the amount of residual dispersion mediumremaining in the active material layer 5 was large, so the activematerial layer 5 was presumably in a half-dried state.

As described above, in the electrode sheet drying apparatus 100, bandhot air HA blown toward the obliquely upstream side IH from the nozzle133 of each of the hot air blowers 130 travels toward the upstream sideCH1 in the conveying direction CH along the undried active materiallayer 5 x or the undried active material layer 15 x over the longdistance L, specifically, over the distance LS longer than or equal to15 times as large as the gap G from the first upstream-side edge 134 ntof the nozzle 133 to the undried active material layer 5 x or theundried active material layer 15 x. Therefore, it is possible toefficiently dry the undried active material layer 5 x or the undriedactive material layer 15 x.

Moreover, each hot air blower 130 does not need a spread prevention part(for example, the second wall 931 b in FIG. 9) that prevents the spreadof band hot air HA in the first thickness direction GH1 (the directionto separate from the undried active material layer 5 x) on the upstreamside CH1 of the nozzle 133. Therefore, in comparison with a hot airblower having a spread prevention part (for example, the hot air blower930 shown in FIG. 9), the size La (see FIG. 5) of the overall hot airblower 130 in the conveying direction CH is reduced. For this reason,the flexibility of arrangement of hot air blowers 130 is increased, forexample, the size of the electrode sheet drying apparatus 100 in theconveying direction CH is reduced by arranging the plurality of hot airblowers 130 at a narrow pitch.

In addition, in the electrode sheet drying apparatus 100, the angle α(the angle α formed between each of the first guide surface 134 n andthe second guide surface 135 n and the undried active material layer 5x) of each nozzle 133 is set to a value that falls within a range from5° to 45°, the gap G from the first upstream-side edge 134 nt of thenozzle 133 to the undried active material layer 5 x or the undriedactive material layer 15 x is set to a value that falls within a rangefrom 3 mm to 10 mm, and the initial flow velocity Vs of band hot air HAis set to a value that falls within a range from 40 m/s to 80 m/s. Withthis configuration, band hot air HA blown from the nozzle 133 tends toflow toward the upstream side CH1 along the undried active materiallayer 5 x or the undried active material layer 15 x over the longdistance L.

The disclosure is described based on the embodiment; however, thedisclosure is not limited to the embodiment. Of course, the embodimentmay be modified as needed without departing from the purport of thedisclosure.

What is claimed is:
 1. An electrode sheet drying apparatus that heatsand dries an undried active material layer provided on a band currentcollector foil in an undried electrode sheet while conveying the undriedelectrode sheet in a longitudinal direction of the undried electrodesheet, the electrode sheet drying apparatus comprising: a plurality ofhot air blowers each located in a first thickness direction with respectto the undried electrode sheet, the first thickness direction beingdirected from the current collector foil toward the undried activematerial layer in a thickness direction of the undried electrode sheet,the plurality of hot air blowers being arranged in a conveying directionof the undried electrode sheet at a predetermined pitch, wherein: eachof the hot air blowers includes a nozzle configured to blow band hot airin a second thickness direction opposite from the first thicknessdirection in the thickness direction and toward an obliquely upstreamside that is an upstream side in the conveying direction, the band hotair spreading in a width direction of the undried electrode sheet; thenozzle includes a first hot air guide having a first guide surface thatadvances in the first thickness direction toward a downstream side inthe conveying direction, and a second hot air guide located in thesecond thickness direction with respect to the first guide surface andhaving a second guide surface facing and parallel to the first guidesurface; the nozzle is configured to blow the band hot air toward theobliquely upstream side from between a first upstream-side edge that isan edge at the upstream side of the first guide surface and a secondupstream-side edge that is an edge at the upstream side of the secondguide surface through between the first guide surface and the secondguide surface; and an angle formed between the first guide surface orthe second guide surface and the undried active material layer is set toan angle at which the blown band hot air travels toward the upstreamside along the undried active material layer over a distance longer thanor equal to 15 times as large as a gap from the first upstream-side edgeto the undried active material layer even without a spread preventionpart that prevents spread of the band hot air in the first thicknessdirection being provided on the upstream side of the nozzle.
 2. Theelectrode sheet drying apparatus according to claim 1, wherein: theangle falls within a range from 5° to 45°; the gap falls within a rangefrom 3 mm to 10 mm; and an initial flow velocity of the band hot airblown from the nozzle falls within a range from 40 m/s to 80 m/s.